This invention relates to a steering system for motor vehicles and in particular for heavy duty trucks having a plurality of controllable wheels or axles and wherein the steering of said wheels or axles takes place by comparison of a desired to an actual position signal and a force responsive to the difference therebetween to move the wheel to a position whereat the difference signal becomes zero.
Hydraulic steering systems of the above described type are known. The means for furnishing the desired and the actual position signals are mechanically or hydraulically coupled to a comparator. However, such steering systems do not work accurately and the different steering functions cannot readily be exchanged and require a relatively high amount of equipment. On the other hand heavy duty vehicles of the above described type require a rapid and manifold changes in the steering functions so that the vehicle can meet its requirements, that is, be steered in accordance with the curvature of the street in spite of its great length. For example the possibility must exist that the vehicle can be controlled selectively either to drive straight ahead, to drive around a curve or even to drive in a perpendicular direction to its lengthwise axis if required.
Further, it is of course required that the individually controlled wheels or axles all reach the required desired positions in the same time period since otherwise the progress of vehicle will not be smooth. The steering system must thus move the wheels (or the axles connected to the wheels) within the same time period through corresponding angles which, when the vehicle turns around a curve, will not be the same angle for each wheel. The different angles do not under such circumstances have a linear or proportional relationship to each other. Actually the angles of rotation are related by a tangent function while the vehicle is turning. This, of course, for equal time periods requires a tangent time function as well. Thus for each angle the associated time differential must be computed by means of a computer.